Summary: Students make observations and measurements of several water samples. This activity helps students think about different ways to determine water quality.
- 50 minutes or more, depending
- 5 clear glass jars or clear soda bottles with lids
- Instant coffee and/or cocoa, kosher salt, hydrochloric acid, isopropyl alcohol and food coloring (to make a purple color)
- Local river or pond water
- Water quality testing kits that can be used to measure oxygen and pH
- Create water quality jars. Fill the five jars with water. (Jar 5 will be filled with the river water.)
- Jar 1 – Add enough coffee grounds and cocoa powder until the water has a good “dirty” look. Label it jar 1.
- Jar 2 – Add food coloring so that the water appears clear purple. Label it jar 2.
- Jar 3 – Add a trace of hydrochloric acid. The HCl solution should be clear and colorless. Label it jar 3.
- Jar 4 – Add a few tablespoons of kosher table salt. The salt will dissolve in the water, resulting in a clear, colorless solution. Label it jar 4.
- Jar 5 – Fill a jar or bottle with water from your local river. Label it jar 5.
In small groups:
- Ask students to examine the water sample jars. You may choose to have students record their observations on the Water Quality Worksheet or in their notebooks.
- Ask groups of students to work together to determine which of the water samples they would be willing to use for such things as fishing, swimming, boating or drinking.
- After students have observed all the jars, have them share their consensus and rationale for their decisions regarding water use. Prompt students to provide evidence for their decisions. (You may also choose to record the class data in a chart.)
- Using this shared experience, facilitate a discussion that leads to an agreed upon definition of “water quality.”
- Have students brainstorm answers to the following questions:
- What is meant by quality?
- What is water quality?
- How can we determine water quality?
- Why is water quality important to us and to other animals?
- How did we determine water quality for the bottles?
- Are these methods trustworthy?
- How else could we measure water quality?
- How might scientists measure water quality?
- Introduce the concepts of dissolved oxygen and pH. Explain what numerical values for each are necessary for life. Explain that scientists use these numerical values to measure water quality.
- Use one of the water samples from before to demonstrate how each test is conducted.
- Allow groups of students to measure oxygen and pH for the other water samples. Summarize the results on the board. Discuss the results from a scientist’s perspective. Which sample has the highest quality based on this data?
- Discuss whether these results are consistent with the determinations made just by looking at the water.
- Explain that water quality is a complex concept and there are many other variables that scientists use to measure it. Explain that you can’t tell true water quality just by looking at it.
Provide students with articles from newspapers that refer to the water quality of local rivers.
- Choose articles that address living organisms in the water or human uses of the water.
- Describe how members of the community talk about their river or what actions they’re taking to prevent or reduce water quality problems.
Used with permission: Center for Highly Interactive Classrooms, Curricula and Computing in Education (Hi-ce), University of Michigan School of Education.